Factors influencing the resealing of human erythrocytes following osmotic lysis are being studied. Resealing depends upon the conditions of lysis. Its kinetics are being followed by incorporating molecules of various sizes into the ghosts during resealing. The role of small molecules such as ATP and of the removal and addition of protein and lipid components of the membrane are being examined. Affinity labeling and protection of proteolytically reactive regions of the membrane with nucleotides will be used to examine the sites of nucleotide interaction. Aging has a deleterious effect upon resealing. Various fresh components will be added to see if they alter this effect. Electrophoretic analysis of invertebrate red cell membranes is in progress to compare primitive membranes with those from more evolved cell types.